Pythium root rot is one of the most common diseases of commercially grown poinsettia and P. aphanidermatum is the predominant species causing pythium root rot in North Carolina ( Lookabaugh et al., 2015 ). Under favorable environmental conditions
most popular holiday flowers worldwide, limiting the losses of poinsettia plants from disease is critical to production ( Lookabaugh et al. 2020 ). Pythium aphanidermatum is a recurrent disease and the predominant Pythium species causing poinsettia
Meloidogyne javanica and Pythium aphanidermatum in greenhouse trials. In the second series of greenhouse trials, factorial experiments were conducted to determine effects of M. javanica and P. aphanidermatum, alone and in combination, on four different
Forty-one cultivars of triploid and diploid watermelons (Citrullus lanatus) were grown at Lane, Oklahoma in 2003. Seeds were placed in Jiffy-9 pellets in a greenhouse on 21 May. Fields were prepared with raised beds 1 m wide covered with black plastic. Plots were 3 m wide by 15 m long, with 4 replications, arranged as a randomized complete block. Seedlings were transplanted to the field on 4 June. From 4–9 June, rainfall occurred 5 days. Maximum soil temperatures at 5 cm, under bare soil, from 1–9 June were 34, 34, 35, 26, 22, 26, 31, 29, and 32 °C, respectively. On 9 June, 84% of the seedlings were dead. Lesions were observed on the roots and stems and isolations were made from symptomatic tissues. The predominant pathogen isolated from the seedlings was Pythium aphanidermatum. Some of the cultivars appear to have some degree of resistance to P. aphanidermatum. Mortality among the cultivars, averaged across all replications, ranged from 33% to 100%. The cultivars with the lowest mortality were “Tri-X Carousel” (33%), `Sunny' (40%), `WT-02-31' (53%), `Ole' (58%), and `Tri-X Palomar' (68%). New seeds were seeded in the greenhouse on 16 June, and transplanted to the field on June 30. The replacement seedlings were planted in the same field, in the same location as the previous plants. Maximum soil temperatures for the two week interval following the second planting ranged from 33 to 39 °C, with only one rain of 0.8 cm occurring 10 days after planting. There was no apparent plant loss due to P. aphidermatum in the second planting.
were diluted to different concentrations with distilled water. Plant pathogenic fungi isolation, purification, and preservation. Pythium aphanidermatum was originally isolated from papaya plants exhibiting symptoms of seedling damping-off in a
A simple field Pythium inoculation technique is needed to be able to assess cultivars for disease resistance and effectiveness of cultural practices or fungicides in the management of Pythium blight. We assessed two mixtures as inocula [i.e., an infested tall fescue (Festuca arundinacea Schreb.) seed plus wheat (Triticum aestivum L.) bran and an infested rye (Secale cereale L.) plus barley (Hordeum vulgare L.) grain mix], and three covers (black and clear plastic, and a geothermal blanket) for their ease of use and consistency in producing Pythium blight epidemics in perennial ryegrass (Lolium perenne L.) field plots. Both the fescue seed-wheat bran and rye-barley grain inocula provided good media on which to culture Pythium aphanidermatum (Edson) Fitzp. In general, the fescue-wheat bran mix applied at the high level (100 mL/0.9-m2 plots) produced greater blight ratings in perennial ryegrass than did the low level (50 mL/0.9-m2 plot). The fescue-wheat bran also was generally more effective than either rate of the rye-barley mix in blighting turf. All covers enhanced blighting, when compared to the uncovered control, by raising the relative humidity. Covering plots with black plastic following inoculation resulted in greater blight ratings than did covering with either clear plastic or the geothermal blanket.
`Embryonic axes-derived `Burpless Hybrid' cucumber (Cucumis sativus L.) plantlets germinated on Murashige and Skoog (MS) medium supplemented with 16 combinations of BAP and NAA and seedlings derived from whole seeds cultured on semi-solid agar were inoculated in vitro with two isolates (WFU3 and WFM13) of Pythium aphanidermatum. All axes-derived plantlets and whole seedlings inoculated with WFM13 isolates were susceptible to blight and died 2 days after inoculation. Similarly, all seedlings inoculated with WFU3 isolates were killed within 2 days after inoculation; however, the rate of development and severity of blight varied among the axes-derived plantlets. Blight on axes-derived plantlets, regenerated on MS medium supplemented with 2 mg BAP/liter and 0.2 mg NAA/liter, was significantly less than on regenerants cultured on all other amended MS media. On some media, callus developed on crowns and/or primary roots. The presence of callus influenced resistance to Pythium. In a second experiment, axes-derived cucumber regenerants from five genotypes, cultured on MS medium supplemented with 2 mg BAP/liter and 0.2 mg N&A/liter, were compared for their resistance to P. aphanidermatum isolate WFU3. Resistance was significantly greater for `Burpless Hybrid' and `Sweetslice' than for three other genotypes. Chemical names used: 6-benzylaminopurine (BAP); α -naphthaleneacetic acid (NAA).
Two experiments were conducted in separate locations, one at Université Laval in eastern Canada (Québec) and one at the Agassiz Research Station in western Canada (British Columbia), in an attempt to determine the effectiveness of soluble silicon (Si) against cucumber root disease caused by Pythium aphanidermatum Edson. Long English cucumber (Cucumis sativus L. cv. Corona) plants were grown either in a standard nutrient solution or in nutrient solutions supplemented with 1.7 mm (100 ppm) Si and inoculated or not with the pathogen. Supplying the solutions with 1.7 mm Si significantly reduced mortality and disease symptoms attributed to infection by P. aphanidermatum. Grown in presence of Si, plants infected with P. aphanidermatum showed a significant increase in yield, marketable fruit, and plant dry weight compared to Si-nonamended and infected plants. These beneficial effects were observed under both experimental conditions. The fruit yield of noninoculated plants was not affected by the presence of Si in the Agassiz experiment. However, Si-amended control plants were more productive in the experiment conducted at Laval, apparently because of contamination problems, which indicates that Si beneficial effects are most likely related to disease management.
incidence of Pythium spp. in floriculture crops was reported in Pennsylvania in 2002 ( Moorman et al., 2002 ): P. irregulare and P. aphanidermatum were the most common species. In Michigan, it was found that P. irregulare , P. ultimum , and P
crops in the northeastern United States were used for this study, Pythium aphanidermatum (Edson) Fitzp., P. cryptoirregulare (Garzón, Yánez, and Moorman), and P. irregulare Buisman. Cultures were maintained on colonized water agar (WA) blocks in